The present invention relates generally to communications in a multi-rate capable communication system, such as a WLAN (wireless local area network) operable generally pursuant to the IEEE 802.11 standard. More particularly, the present invention relates to an apparatus, and an associated method, by which to broadcast beacon signals to mobile stations operable in the radio communication system. Broadcast of the beacon signals according to an embodiment of the present invention facilitates efficient usage of bandwidth allocated for communication in a radio communication system, thereby to permit increased efficiency of communications in the radio communication system.
A communication system provides for communication of information between a sending station and a receiving station by way of a communication channel. Information to be communicated by the sending station to the receiving station is converted into a form to permit its communication upon the communication channel. A wide variety of different types of communication systems have been developed and are regularly utilized to effectuate communication of information between sending and receiving stations.
New types of communication systems have been, and continue to be, developed and constructed as a result of advancements in communication technologies. A radio communication system is representative of a type of communication system which has benefited from advancements in communication technologies. Increased communication mobility is provided in a radio communication system as radio-links are utilized to form communication channels in a radio communication system in contrast to the conventional need to utilize wireline connections.
The communication capacity of a radio communication system, however, is sometimes constricted by bandwidth limitations. Only a limited amount of the electromagnetic spectrum is allocated to be used by a particular radio communication system. In other words, when the communication capacity is limited by the bandwidth allocated to the radio communication system, an increase in communication capacity requires more efficient utilization of the allocated bandwidth.
Digital communication techniques, for instance, can be used in a manner by which to increase the bandwidth efficiency of communications upon a communication channel in a communication system. Due to the particular need to efficiently utilize the bandwidth allocated in the radio communication system, the use of such digital techniques is particularly advantageously utilized in a radio communication system.
Digital communication techniques typically involve digitizing information, i.e., data, which is to be communicated into digital form to form digital bits. The digitized bits are sometimes then formatted into sequences which form packets of which one or more packets together form a frame. The terms packet and frame shall be, at times, used interchangeably herein to refer generally to digital data which is to be communicated. The sequences of the data forming the packets or frames can be communicated at discrete intervals and thereafter connected theretogether to recreate the informational content of the data.
Because packets or frames of data can be communicated at discrete intervals, a frequency band need not be dedicated solely for the communication of data generated by one sending station for transmission to one receiving station, as conventionally required in analog communications. Instead, the frequency band can be shared amongst a plurality of different sending and receiving station pairs. Because the same frequency band can be utilized to effectuate communications by the plurality of pairs of communication stations, improved communication capacity is possible.
Conventional LANs communicate packets of data to effectuate communications therein. Wireless networks, operable in manners analogous LANs, referred to as WLANs (wireless local area networks) have also been developed and are utilized to communicate data over a radio-link.
The standards of operation of an exemplary WLAN are set forth in the IEEE (Institute of Electrical and Electronic Engineers) 802.11 specification. The standard set forth in the specification provides for multi-user communications. Data is formatted into frames and sent over a radio-link.
As presently-promulgated, the IEEE 802.11 specification defines a contention period (CP) and contention free period (CFP). The contention period defines a random access period during which any sending station is permitted random access to communicate a frame of data. And, the contention free period defines a period in which data is permitted to be communicated responsive to a polling procedure in which allocations are made as to when a sending station is permitted to communicate a frame of data.
The specification, as presently-promulgated, requires that the contention free period be initiated by the broadcast of a beacon signal. And, subsequent beacon signals are broadcast at a beacon interval. A beacon frame is sent during the contention period (CP) as well as the contention free period (CFP). The beacon signal is utilized, amongst other things, for purposes of synchronization of mobile stations operable in the system.
As presently-promulgated, the specification requires that the beacon signals be transmitted at a lowest mandatory rate to insure that all mobile stations operable in the system are able to detect and utilize the informational content of the beacon signal. This existing requirement to broadcast always the beacon signal at the lowest mandatory rate can be an inefficient use of the limited bandwidth.
For instance, if the lowest mandatory rate is a bit rate of 1 Mb/s and in an example situation having eleven mobile stations in which ten mobile stations are operable at a much higher bit rate, e.g., 11 Mb/s, and only one mobile station is operable at the lower bit rate of 1 Mb/s, all of the beacon signals are broadcast at the 1 Mb/s data rate. As the majority of mobile stations are operable at a much higher data rate, the existing requirement of transmitting each of the beacon signals at the lower data rate inefficiently utilizes the limited time available within a contention free period within which to communicate information.
If a manner could be provided by which to broadcast beacon signals in a more efficient manner, improved communication efficiency would result.
It is in light of this background information related to multi-rate, multi-user communication systems that the significant improvements of the present invention have evolved.
The present invention, accordingly, advantageously provides apparatus and an associated method, by which to transmit beacon signals broadcast to mobile stations operable in a radio communication system such as a (wireless local area network) operable pursuant to an IEEE 802.11 standard.
Operation of an embodiment of the present invention permits increased communication efficiency by selectably broadcasting beacon signals at higher bit rates than a minimum allowable bit rate.
In one aspect of the present invention, a first beacon signal is broadcast to initiate a contention free period (CFP). The first beacon signal is broadcast at a lowest allowable rate to ensure that every mobile station operable in the communication system is able to detect the content of the beacon signal. Subsequent beacon signals are generated at a beacon interval, and subsequent beacon signals are generated at data rates corresponding to the data rates at which subsequent communications are to be effectuated. The communications are sorted such that communications to be effectuated at higher data rates are effectuated first. Thereby, the beacon signal generated immediately subsequent to the first beacon signal is generated at a data rate corresponding to the highest data rate at which communications shall be effectuated during the contention free period. Thereafter, a subsequent beacon signal is generated at a next-to-highest data rate at which communications are to be effectuated during the contention free period. Additional beacon signals are generated at the next-to-highest data rate, or lower, depending upon the data rates at which communications are to be effectuated with remaining ones of the mobile stations.
Because beacon signals are broadcast at higher-than-minimum data rates, additional portions of the contention free period can be utilized for the communication of data. That is to say, by broadcasting beacon signals are higher data rates, lessened amounts of time need to be dedicated for such transmissions. A greater proportion of the contention free period is instead utilized for up-link and down-link transmissions of communications.
An embodiment of the present invention is operable in any of various communication systems. In the exemplary implementation, an embodiment of the present invention is operable in a (wireless local area network) constructed pursuant to the IEEE 802.11 standard. As set forth in the standard for WLAN activity at a MAC (medium access control) layer, beacon signals are caused to be broadcast at beacon intervals. In operation of an embodiment of the present invention, the point coordination function selects the data rate at which a beacon signal is to be broadcast responsive to the capabilities of the mobile stations which are to communicate data during the contention free period by providing such data rates selectability to the beacon signals, the contention free period can be used more efficiently, thereby to permit increased efficiency of communications in the communication system.
In one implementation, an access point (AP) forming a portion of the network infrastructure of the WLAN controls communications during the contention free period. A beacon signal is broadcast to initiate the contention free period. The initial beacon signal is broadcast at a lowest allowable data rate in conventional manner. Sorting is performed at the access point to cause communications which are effectuable at higher data rates to be performed prior to effectuation of communications at lower data rates. Beacon signals broadcast at beacon intervals when communications are being effectuated at the higher data rates are broadcast at correspondingly higher data rates. The time otherwise required to broadcast the beacon signals are the lowest permitted data rate is utilized for other purposes. For instance, such time can be utilized to perform retransmission of missed frames within the same contention free period.
A more efficient manner by which to perform communications during the contention free period is thereby provided. Fuller advantage provided by a multi-rate communication system is permitted.
In these and other aspects, therefore, apparatus, and an associated method, is provided for a radio communication system having a network infrastructure with which a first mobile station and at least a second mobile station communicates data. The first mobile station is selected to be communicated at a first data rate and the data to be communicated between the network infrastructure and the second mobile station is selected to be communicated at a second data rate. A beacon signal generator is coupled to receive indications of the first data rate and the second data rate at which the data is selected to be communicated between the network infrastructure and the first mobile station and between the network infrastructure and the second mobile station. The beacon signal signals a first beacon signal and at least a second beacon signal within a selected time period. The first beacon signal is generated at a rate at least as low as the lowest of the first selected rate and the second beacon signal is generated at a rate corresponding to a highest of the first selected rate and the at least second selected rate.
A more complete appreciation of the present invention and the scope thereof can be obtained from the accompanying drawings which are briefly summarized below, the following detailed description of the presently-preferred embodiments of the invention, and the appended claims.